The failure of C14-formate to affect the course of mouse leukemia.

eral, localizing substances of adequate selectivity that can be labeled and used for radiotherapy have not been discovered. If such are found, it would be desirable that they carry a radioactive isotope which emits a very soft ray, such as iH3 or eC14. Even these emit beta-rays that traverse several cell diameters; however, the half penetration of the iH3 beta-ray is less than the radius of the aver age cell." The incorporation of formate carbon into the 2and 8-positions of the uric acid skeleton was first observed by Sonne, Buchanan, and Delluva (4). Totter et al. (5) have shown that, likewise in the rat, formate is a precursor of desoxyribonucleic acid guanine, adenine, and thymine (methyl car bon) and ribonucleic acid guanine and adenine. We have confirmed these latter observations many times in the mouse.1